Can I use the mineral oil already in the compressor assuming the system is built such that the oil has no where to go but return to the compressor, or should i drain it out and use poe or pao oil.

second question is: the line dryer on the compressor isn't easily replaced and i'm wondering how long you think it would take to dry it out if i pull a vacuum on the system while heating the compressor and line dryer to 200F or so. 24 hours, a week? the compressor has been used as an air compressor for some time btw, so it will need to get baked out.